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Chapter 10
ADO
What is ADO?
•What is ADO?
•ADO is a Microsoft technology
•ADO stands for ActiveX Data Objects
•ADO is a programming interface to access data in a
database
What is ADO?
•ADO.NET is an object-oriented set of libraries
that allows you to interact with data sources.
•Commonly, the data source is a database, but
it could also be a text file, an Excel
spreadsheet, or an XML file.
Data Providers
•
ADO.NET allows us to interact with different types
of data sources and different types of databases.
•
There isn't a single set of classes that allow you to
accomplish this universally.
•
Different data sources expose different protocols.
•
Some older data sources use the ODBC protocol,
many newer data sources use the OleDb protocol
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Data Providers
Provider Name
API
prefix
Data Source Description
ODBC Data
Provider
Odbc
Data Sources with an ODBC interface. Normally older data bases.
OleDb Data
Provider
OleDb
Data Sources that expose an OleDb interface, i.e. Access or Excel.
Oracle Data
Provider
Oracle
For Oracle Databases.
SQL Data
Provider
Sql
For interacting with Microsoft SQL Server.
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ADO.NET Objects
•Connection Object
•Command Object
•DataReader
•DataSet
•DataAdapter
Connection Object
•To interact with a database, you must have a connection
to it.
•The connection helps identify the database server, the
database name, user name, password, and other
parameters that are required for connecting to the data
base.
• A connection object is used by command objects so they
will know which database to execute the command on.
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Command Object
•You use a command object to send SQL statements to the
database.
•A command object uses a connection object to figure out
which database to communicate with.
•You can use a command object alone, to execute a
command directly, or assign a reference to a command
object to a DataAdapter, which holds a set of commands
that work on a group of data as described below.
DataReader
•Many data operations require that you only get a stream of data for
reading.
•The data reader object allows you to obtain the results of a SELECT
statement from a command object.
•For performance reasons, the data returned from a data reader is a
fast forward-only stream of data.
•This means that you can only pull the data from the stream in a
sequential manner This is good for speed, but if you need to
manipulate data, then a DataSet is a better object to work with.
DataSets
•DataSet objects are in-memory representations of data.
•They contain multiple Datatable objects, which contain
columns and rows.
•You can even define relations between tables to create
parent-child relationships.
DataAdapter
•The data adapter helps to manage data in a disconnected mode.
• The data adapter fills a DataSet object when reading the data and
writes in a single batch when persisting changes back to the
database.
•A data adapter contains a reference to the connection object and
opens and closes the connection automatically when reading from
or writing to the database.
•Additionally, the data adapter contains command object
references for SELECT, INSERT, UPDATE, and DELETE operations on
the data.
Using a Connection
•The purpose of creating a Connection object is so you can
enable other ADO.NET code to work with a database.
•Other ADO.NET objects, such as a Command and a DataAdapter
take a connection object as a parameter.
•
•
•
•
•
Instantiate the Connection.
Open the connection.
Pass the connection to other ADO.NET objects.
Perform database operations with the other ADO.NET objects.
Close the connection.
Using Command Objects
•A SqlCommand object allows you to query and send
commands to a database.
•It has methods that are specialized for different
commands.
•The ExecuteReader method returns a DataReader object
for viewing the results of a select query.
• For insert, update, and delete SQL commands, you use
the ExecuteNonQuery method.
•If you only need a single aggregate value from a query,
the ExecuteScalar is the best choice
DataReader Objects
•A DataReader is a type that is good for reading data in the most
efficient manner possible. You can *not* use it for writing data.
•You can read from DataReader objects in a forward-only
sequential manner. Once you've read some data, you must save
it because you will not be able to go back and read it again.
DataSets and DataAdapters
•A DataSet is an in-memory data store that can hold
numerous tables. DataSets only hold data and do not
interact with a data source.
•It is the DataAdapter that manages connections with the
data source and gives us disconnected behavior.
•The DataAdapter opens a connection only when required
and closes it as soon as it has performed its task.
DataAdapters
•A DataAdapter performs the following tasks when filling a
DataSet with data:
• Open connection
• Retrieve data into DataSet
• Close connection
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